In order to comply with present and future environmental legislation, current vehicles are provided with anti-Particulate Filters which are devices located in the exhaust line of the engine designed to trap the soot in order to clean the exhaust gas. Electronics systems managing the engine are capable to recognize when the filter is full; at this time they command a so-called regeneration process: this is, in principle, a process to empty out the filter based on soot auto-combustion inside the filter itself. Filter regeneration is achieved by an exhaust gas temperature increase (up to 630° C. or more) for a short time (around 10 minutes).
In order to achieve the needed temperature for regenerating the anti-Particulate Filter, so called post injections are employed; these are fuel injections that are activated during the regeneration process and that occur after the Top Dead Center (TDC) of the piston. These post injections, since they occur very far from the TDC, represent a contribution to HydroCarbon (HC) exhaust content. Due to these phenomena, fuel from post injections more likely hits and wets the walls of the combustion chamber and is adsorbed to the oil, causing a decrease of the oil viscosity.
On the contrary, during normal operation of the engine, some of the fuel HydroCarbons (HC) previously adsorbed inside the oil evaporate, causing an increase of oil viscosity. The intensity of both these phenomena depends on the engine and vehicle working conditions, which can be summarized as vehicle Mission Profiles. Also, these phenomena have an impact on engine oil life and contribute to determine the necessity of oil change.
Excessively low viscosity of the oil can lead to engine damage. Also, an inaccurate estimation of oil viscosity can lead to unnecessary high rate of oil change events.
Current methods used for the estimation of oil viscosity only consider a constant oil dilution rate and a constant HydroCarbons (HC) evaporation rate in every working condition of the engine. Also, these methods do not consider the limitation of the evaporation phase that may occur due to a saturation in the physical phenomena. Finally these methods do not take into account the history of the oil in the engine that is relevant especially after a certain number of particulate filter regeneration events. Due to these factors, current methods exhibit a behavior that does not appear sufficiently accurate.
At least one object is obtain an improvement in the estimation of engine oil viscosity that provides a more accurate oil viscosity information for a variety of uses. At least a further object is to use such improved estimation to greatly reduce the risk of engine failure or damage due to insufficient oil viscosity. At least another object is to provide such accurate oil viscosity information without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle. Yet another object of the present disclosure is to meet these goals by means of a rather simple, rational and inexpensive solution. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.